Spatial databases store geographical and topological data to support map rendering and navigational applications. A major consideration when rendering spatial data is to decide which layers to display at a particular zoom level on a map. For example, a layer may include very detailed polygonal features with about 3000 features in each polygon. When the zoom level is very far away (e.g., “zoomed out”), the preferred practice is not display these very detailed polygons because the detail of the polygons is lost due to the limited resolution of the display. Many of the polygon vertices are rendered onto just a few display pixels. In addition, transferring the large number of vertices associated with detailed polygonal features at a high zoom level can introduce a network bottleneck.
A more realistic scenario is to use zoom control to only “turn on” the detailed polygons when reasonably zoomed in, and to display a generalized, less detailed representation of the polygons when zoomed further out. This can be accomplished by generating a generalized version of the detailed polygon layer. The generalized layer is displayed when the display is zoomed out. Correct usage of zoom control and generalized layers can produce better map generation performance.